1. Field of the Invention
The present invention relates to a converter control device that controls a highly-efficient converter installed in an air conditioner and an air conditioner including the converter control device.
2. Description of the Related Art
There is known a conventional converter control device that obtains a rectified voltage by rectifying an alternate-current power source voltage with a rectifying circuit such as a diode bridge, and improves the power factor using a voltage-boosting reactor and a semiconductor switching element such as a metal-oxide semiconductor field-effect transistor (MOSFET) that is on/off controlled by pulse width modulation (PWM) control. The PWM control of the semiconductor switching element is executed using a triangular wave signal having a constant fundamental switching frequency, and therefore a frequency component of conduction noise caused with the on/off operation of the semiconductor switching element has large peak values at frequencies of integer multiples of the fundamental switching frequency. In addition, because a conducting path of the conduction noise is complicated, an anti-noise measure to prevent noise propagation and leakage to other parts is also complicated. Therefore, in order to achieve design considering a measure to strain the amount of caused noise, the designing needs to be performed with setting a design reference level with a sufficient margin with respect to domestic and international standards related to radiated noise. This design style causes increase of a manufacturing cost, such as increase in size of an anti-noise measure part and increase of the number of parts.
In connection thereto, there has been a converter control device that reduces a peak value of noise by distributing a frequency component of caused noise in such a way that a fundamental switching frequency of a driving signal for on/off controlling a semiconductor switching element is variably controlled based on an absolute value of an alternate-current power source voltage (see, for example, Japanese Patent Application Laid-open No. 2004-282958 [Patent Literature 1]).
In the conventional converter control device, because the on/off control of the semiconductor switching element is executed with a switching operation using a fixed frequency (fundamental switching frequency), the electromagnetic conduction noise caused due to the switching operation has large peaks in frequency components at the integer multiples of the fundamental switching frequency. On the other hand, an electric appliance such as an air conditioner needs to meet the Noise Terminal Voltage Standards (Electrical Appliance and Material Safety Law, the Standard in Article 2 or the like of the Ministerial Ordinance) in order to restrain noise leaked from the appliance. Therefore, when designing electric appliances, noise filters for limiting conduction noise need to be connected in a multi-stage configuration using a large number of noise filter parts, and this causes a problem of increasing a those parts' occupying area in a board and also increasing the manufacturing cost.
The converter control device described in Patent Literature 1 executes control of “setting a switching frequency f of a main switch Q1 to a lower-limit frequency f12 (for example, 20 kHz) when an alternate-current power source voltage Vi is equal to or smaller than a lower-limit setting voltage EB”, “setting the switching frequency f of the main switch Q1 to an upper-limit frequency f11 (for example, 100 kHz) when the alternate-current power source voltage Vi is equal to or larger than an upper-limit setting voltage (VZ+EB)”, and “gradually changing the switching frequency f from the lower-limit frequency f12 to the upper-limit frequency f11 when the alternate-current power source voltage Vi is in a range between the lower-limit setting voltage EB and the upper-limit setting voltage (VZ+EB)”, and therefore the switching frequency is increased in proportion to the value of the alternate-current power source voltage.
Generally, switching noise of a semiconductor element tends to increase as an alternate-current power source voltage becomes higher. On the other hand, the power factor tends to be improved so that the power conversion efficiency is enhanced as the switching frequency is higher, because the current waveform can be close to the alternate-current voltage waveform as the switching frequency is higher. Therefore, in the control described in Patent Literature 1, the caused noise is increased although the power conversion efficiency is enhanced, and there has been a problem in that it is not possible to execute the control while considering both of the amount of caused noise and loss generation that are in a tradeoff relationship with each other.
The present invention has been achieved to solve the above problems, and a first object of the present invention is to provide a converter control device that can achieve control while considering both the amount of caused noise and loss generation in a converter. A second object of the present invention is to provide an air conditioner that includes a convertor control device that executes control while considering both the amount of caused noise and loss generation and can perform operation control considering both the noise generation and loss generation.